Go slow. Read directions from several places several times, and get a quality bit made to drill glass. Glass-holes.com lists the saw you need for the size bulkhead you want to have, and they sell the cool black bulkheads, too.
I have a 125 gallon sump, drip 40 gallon per day, and my drain in my sump is just a 3/4 inch PVC going out through the wall.
I drilled my sump halfway between the top and bottom of the sump. And I have an elbow and a short PVC piece inside the sump to fine tune sump water level--a standpipe that's easy to shorten.